Such a switch is known from US patent application US 2006/0278516. The known electrical switch device comprises a body upon which is mounted a hand lever that rotates about a main axis, cooperating with a transmission shaft able to control the opening or the closing of electrical contacts of the electrical switch device and elastic linking means between the hand lever and the transmission shaft. The device also comprises means for locking the rotation of the hand lever with respect to the body, used when an angular divergence between the hand lever and the transmission shaft exceeds a specified threshold. The purpose of the know patent application is to limit the damage to the hand lever and to the electrical device when an operator attempts to return the hand lever to its “OFF” position whilst the contacts are welded and to prevent the beginning of electrical arcing if the operator should succeed in unsticking the contacts when rotating the hand lever.
The known switch has the disadvantage that its function relies fully on the performance of the elastic linking means, which shall be stiff enough for joining together the rotation of the hand lever and the shaft support in normal operation, and at the same time flex sufficiently when a rotational torque is applied to the hand lever while the shaft support is immobilized due to a welding between the contacts. These essentially conflicting requirements can cause the locking mechanism to malfunction after repetitive use, with the effect that a dangerous situation can arise in which it is possible to rotate the hand level to an “OFF”-position while the contacts are still closed, i.e., actually in the “ON”-position. It is a further disadvantage of the known switch that it puts tight requirements on the strength of the locking device, its corresponding parts in the body of the switch (the teeth) and the protuberance of the hand lever. This limits the maximum force that the device can withstand when the operator tries with a lot of force to unstick the contacts by applying a large rotational torque on the hand lever. Moreover, the known switch does not guarantee that the position of the hand lever is always clearly indicating whether the switch is actually “ON” or “OFF”, i.e., when the contacts are closed or open respectively.